The invention relates to a delivery valve comprising a valve seat and a spring-biased closing member having a return-flow collar and a control collar. In such a delivery valve known from German Auslegesschrift 1,236,863, the return-flow collar is separated by an annular groove from the collar which has at least one recess, in the present case two. This recess is designed as a ground portion and remains within the passage bore in every position of the closing member of the delivery valve. The closing member has a conical sealing face at the end located on the same side as the pump working space and, on the same side as the spring space, a fixed stop, against which it abuts during each of its opening strokes when the compression spring used is of a very soft type. The recess which is provided on the closing member and which thus always has a constant cross-sectional area is designed as a throttle cross-sectional area. The object of this throttle cross-sectional area is to move the delivery-valve closing member into its closing position more quickly at the end of injection, after the closing of the injection nozzle, since the pressure waves reflected in the delivery conduit impinge on the throttle cross-sectional creating, a resistance which has the effect of a closing force acting on the closing member in addition to the compression spring. Because of the different feed rates or feed speeds of the fuel through the delivery valve or the feed line during idling, on the one hand, and under full load at high engine speed, on the other hand, the effect of the throttle on the closing movement of the closing member decreases towards idling, since the pressure wave is relatively weak, that is to say the throttle cross-sectional area provides a lower resistance to this pressure wave and more fuel can flow off through the throttle per unit of time. The closing member is closed correspondingly more slowly, and therefore a larger proportion of the delivery conduit volume is filled through the closing valve with fuel from the pump working space during idling than under full or partial load, so that the pressure reduction in the delivery conduit varies from a minimum amount during idling to a maximum amount under full load.
Such a delivery valve thus serves for controlling the residual pressure in the delivery conduit and for adjusting the fuel feed rate as a function of the injection quantity and the engine speed. At the same time, the throttle operational during the shut-off surge influences the injection rate during the delivery phase of the fuel-injection pump and reduces the fuel-injection quantity under full load with an increase in engine speed.
In known delivery valves, in which the closing member has a return-flow collar and does not run against a fixed stop during each deliver operation, the passage-bore cross-sectional area adjacent to the return-flow collar on the same side as the pump working space and opened by the closing member, is very large, in particular larger than the free cross-sectional area of the adjoining delivery line. In such valves, widely varying injection quantities occur, when the high-pressure delivery of the fuel-injection pump is at a constant setting. Especially in a distributor injection pump, these varying fuel-injection quantities cannot corrected by an appropriate adjustment of the effective delivery stroke of the pump piston, since all the injection points of the internal-combustion engine are supplied alternately from a single pump working space and the quantity control for all the injection points therefore has to be the same, presupposing that there is no injection-quantity control device which controls the injection quantity per delivery stroke of the pump piston individually. However, such a control involves a considerable outlay. Quantities can also be influenced by other secondary measures, such as, for example, stroke limitations of the delivery valve, but this again does not produce the uniform effect desired over the entire operating range of the fuel-injection pump and moreover likewise involves a very high outlay.